Electric switch



p 30, 1953 L. L. CUNNINGHAM 2,854,540

ELECTRIC SWITCH Filed Aug. 15, 1957 ELECTRIC SWITQH Lewis L. Cunningham,Los Altos, fiat-if. Application August 15, 1957, eriai No. 678,423 14Claims. (Cl. Nil-67) This invention relates generally to small enclosedplunger operated electric switches of the type commonly called unitswitches in the electric control industry.

More particularly this invention relates to such a device which willalternately first open at two places one electric circuit then close attwo other places another electric circuit, the device including a firstspaced pair of stationary contacts for the one of the circuits, a secondspaced pair of stationary contacts for the other of the circuits and acontact bridging means for first unbridging one of the pair of contactsand then bridging the other of the pair of contacts.

It is a principal object of. this invention to provide such a switchwhich is snap acting, which can. easily be made'to provide any desiredcontact pressure and in which aminimum of contact bounce will beexperienced in the operation thereof.

It. is a second object to provide such a switch in which substantiallyno circuit current is carried by any'part of the switch' entering intothe mechanical action thereof.

It is a third object to provide such a switch inwhich the open circuitvoltage of acircuit is precisely divided between two simultaneouslyopened gaps when the switch is, opened.

It is a fourth object to provide such a switch in. which asingleresilient moving contact carrying blade is deformed for overcenter action and loosely held to limit contact bounce.

It is a fifth object to provide such a switch in which the movingcontact carrying blade is held rockably about its longitudinalcenterline normal to a plane including its; moving contacts whenever themoving contact carrying blade is in motion to open one circuit and closeanother circuit.

It. is a sixth object to provide such a switch having a single movingcontact blade structure with a shorter part in tension longitudinally ofthe bladeopposed by a longer part in compression longitudinally oftheblade so that the longer part will be bowed away from the plane of the.shorter part, together with means for alternately transversely pressingthe longer part near its midlength through the plane of the shorter partin opposite directions to reverse the forces acting transversely on saidstructure at its ends on said shorter part and at its mid length on saidlonger part.

It isa seventh object to provide such a switch having atmoving contactblade structure with a shorter part in tension longitudinally of theblade opposed by a longer part in-cornpressionlongitudinally of theblade so that the: longer part will be bowed away from the plane of theshorter part, the blade having a pair .of laterally spaced. movingcontacts on an unstressed extension at one. end. thereof pressedvagainst a mating pair of stationary contacts and an other unstressed endextension of the blade. pressed against a. first support pivot on thesame side of the blade as the. stationary contactsby a second supportpivot at the midpoint of said blade-pressing/the outwardlybowedsiderofthe longer part. of the Patented Sept. 30, 1958 ice 2. bladetoward the plane of the shorter part of the blade whereby additionalpressure on the blade in one direction by the first support pivot or in.the other direction by the second support pivot will cause the blade togo over center and remove the moving contacts from bridgmg contact withthe stationary contacts.

It is an eighth object to provide such a switch with three operatingsupport fulcrum means positioned to limit the bow of the compressionpart away from the plane of the tension part whereby by movement of anyof said three fulcrum means toward said blade said compression part maybe moved through the plane of the tension part to relieve all three ofsaid fulcrum means of pressure from said bladeparts.

It is a ninth object to provide such a switch having blade supportingmeans only on one side of the movable blade at any fulcrum point thereofso the blade can not operate as a reed to generate contact bounce.

It is a tenth object to provide such a switch having a moving blade witha supporting pivot means near the midlength thereof, the blade havingunequal moments of inertia of the two ends about said midlength pivotmeans to dampen any natural vibration of the blade ends about saidmidlength pivot means.

How these and other objects are attained is explained in the followingdescription referring to the attached drawing in which Fig. 1 is a planview of a preferred form in which my invention may be practiced.

Fig. 2 is side sectional elevation along the line 2--2 of Fig; 1.

Fig. 3 is a plan view in of Fig. 2.

Fig. 4 is a perspective view of the moving contact blade of the switchof' Figs. 1,2 and 3 Fig. 5 is a side sectional elevation, similar toFig. 2, of an optional form in which my invention may be practiced.

Fig. 6 is a plan View in section along the line -66 of Fig. 5.

Fig. 7 is a perspective view of the moving contact blade of the switchof Figs. 5 and 6.

Like reference numerals,- referto like parts in the several figures ofthe drawing.

Referring now to Figs.v l, 2, 3, and 4 there is shown a form of unitswitch 11 having a hollow molded plastic insulating case split.horizontally along line 3-3 into an upper case part 12 and a lower casepart 13 and held together by screws 14 passed through holes, as shown,in part 12 and threaded into part 13.

Electrically conducting contact rivets 15 are riveted as. shown toswitch terminals 16 and molded into upper case part 12 with silvercontact faces 17 welded to rivets 15 and extending into the hollowspace. 18 formed in case parts 12, 13.

Similarly, electrically conducting contact rivets 19 are riveted asshown to switch terminals 20'and molded into lower case part Iii-withvsilver contact faces 21 welded to rivets 19 and extending into thehollow space 18 formed in case parts 12, 13.

As shown in Figs. 2, 3 and 4; movable contact blade 22 isformed of athin sheet of resilient. metal like spring steel, Phosphor bronze orberylliumv copper and. is split longitudinally on spaced parallel lines.23, 24 with holes 25 at the ends of lines 23, 24' to preventcracking of"the blade in use. Lines 23, 2'4 divide blade 22 into a center section26, two side. sections 27 andtwo end sections.28, 29. Side sections 27are shortened with respect to center section 26 by creasing sidesections 27 as shown at 30. The-sameefiect has been accomplished byswaging center. sectiorn26. to lengthen it, but it has been found thatprecise: control. of the relative lengths of the parts is section alongthe line 3-3 3 obtained more easily by creasing side sections 27 ratherthan to swage center section 26.

With side sections 27 creased as shown at 30, center section 26 islonger and isforcedto bow in longitudinal compression out of the planeof side sections 27 now maintained in .longitudinal tension. Pressureagainst the convex side of bowed center section 26 will cause it 'topass through the plane of sections 27 and change to concave the face ofsection 26 which was previously convex.

Conducting bar 31 is welded to end 28 of blade 22 and movable switchcontacts 32 extending through holes, not shown, in bar 31 and end 28 ofblade 22 are riveted in place as shown. End 29 of blade 22 is slotted asshown at 45 and a hole 33 is formed, as shown, through section 26 ofblade 22. Longitudinally of blade 22, slot 45 and hole 33 are on thecenterline of blade 22 perpendicular to a plane including the centers ofthe four contact faces of contacts 32. Polished metal pin 34, Fig. 2, isnear enough to the diameter of hole 33, Fig. 4, in blade 22 to preventany substantial lateral or longitudinal movement of blade 22 but doesnot interfere with or add friction to the operating movement of blade22. The ends of pin 34 closely fit in holes provided for them in caseparts 12, 13; see Fig. 2. a

Surrounding the ends of pin 34 as they emerge from case parts 12, 13into case interior space 18 are carefully positioned pivot points 35, 36formed on the inner surfaces of case parts 12, 13 as shown. Operatingstem 37 is formed with a pair of spaced pivot points 38, 39 carefullyspaced by a fixed spacing rod 40 adapted loosely to engage blade 22 atslot 45 to prevent rotation of blade 22 about pin 34. As seen in Fig. 2the reduced diameter upper end of stem 37 is freely slidably guided incase part 12 and its full diameter lower end is freely slidably guidedin hole- 41 formed into case part 13. Biasing spring 42 in hole 41normally holds stem 37 upward and the switch operating parts in theirpositions shown in Fig. 2. Shoulder 43 is carefully positioned on stem37 and together with the length of rod 40, the spacing of pivot points35, 36, the spring rate of spring 42, the spacing between contacts 32and contacts 17 and 21, the size of grooves 30 in blade members 27, andthe dimensions of blade 22, determines the switchsensitivity and contactpressure. All of these thingsare determinedby test for a desiredoperating condition and these variables are then fixed for production-It is to be noted that the switch of Figs. 1 to 4, as particularly shownin Figs. 2 and 3, has its blade 22 supported entirely on pivot point 36which presses upwardly on the compression blade section 26 and causesthe movable switch contacts 32 at the ends of conducting bar 31 to pressagainst stationary contacts 17 which are thereby electrically connected.Also the support of blade 22 by pivot point 36 presses the right end ofblade 22, around notch 45, up against pivot point 38 on stem,37. It isseen that blade 22 is held entirely by three fulcrum supports eachspaced from the other and each transversely centered on the same centerline along which they. are each spaced from the other. One of thefulcrum supports of blade 22 when in the position shown in Fig. 2 ismade up of the two transversely aligned stationary. contacts 17 anotheris the fixed pivot point 36 and the third is the movable pivot point 38.

When it is desired to open movable contacts 32 from stationary contacts17, stem 37 is pushed downward to cause pivot point 38 to push downwardaroundrod 40 on the right end of blade 22 and thus to push side sections27 of blade 22 downward along the sides of section 26 of blade 22 whichof course increases the contact pressure uniformly of each of thecontacts 32 on the stationary contacts 17. Further increase of pressureon stem 37 will increase the contact pressures of both contacts 32 oncontacts 17 uniformly until the plane of side sections 27 of blade 22are in the plane of the center section 26 of blade 22 at which time theplane of side sections 22 will suddenly pass to the opposite side of theplane of center section 26 due to the potential energy stored in centersection 26 by the deformation thereof.

It should be particularly noted that as contacts 32 are ready to leavecontacts 17, blade 22 is free to teeter laterally about its longitudinalcenterline and equal pressures will be holding contacts 32 againstcontacts 17 respectively. This condition therefore causes contacts 32 toleave their respective mating contacts 17 simultaneously thus breakingthe open circuit voltage across contacts 17 equally divided between thetwo gaps formed between the two sets of contacts. It is not known thatany prior art device precisely divides this voltage as does this device.I

When the plane of side sections 27 of blade 22 passes the plane ofcenter section 26 center section 26 suddenly goes over center" and snapsupwardly to contact fixed pivot point 35. As the center of centersection 26 throws itself upwards the reaction thereof tends to throw theends of center section 26 downward and carry along with the ends theremainder of blade 22. But the center section 26 being lighter in weightthan the rest of blade 22 the center section at its center moves upwardagainst pivot point 35 first then held by pivot point 35 at its middlesection 26 presses down at its ends to move then downward. Again sincethe weight of blade 22 will not be balanced longitudinally over atransverse center line at pivot point 35 the two ends of blade 22(contacts 32 on one end and the blade around slot 45 at the other), willnot strike their new end fulcrum supports (stationary contacts 21 at oneend and pivot point 39 at the other) at the same time. With either endstriking first any natural vibration of the blade on its resilient part26 will be impeded by the striking of the other end and it has beenfound that contact bounce or erratic contact action is not sensiblypresent in the operation of this switch. It should of course be notedthat if in design test contact bounce or erratic contact action isnoted, adding or subtracting small weights to a selected end of blade 22will eliminate the trouble.

In the form of switch shown in Figs. 1 to 4 it is apparent that theswitch is designed to open one circuit, terminals 16, and-then to closeanother circuit, terminals 20, and alternately to open the terminal 20circuit and close the terminal 16 circuit. As shown in Fig. 2, thisalternating operation of the switch is accomplished by alternatelypressing down on operating stem 37 against the bias of spring 42 andthen releasing stem 37 so that spring 42 can return stem 42 and theswitch blade to its original condition.

But it is also apparent the switch could also be alternately operated byalternately moving terminals 16 downward to cause section 26 of blade 22to go over center and then to move terminals 20 upward to cause section26 to go back over center. And again the switch could as well beoperated by pivot points 35, 36 if they were free to move and pivotpoint 36 were first moved upward to throw contacts 32 downward and thenpivot point 35 is moved downward to throw blade section 26 back overcenter to return the switch to the condition shown in Fig. 2. A switchhaving the last described operation is shown in Figs. 5, 6, and 7wherein moving contacts 321/are connected by bar 311 on end 281 of blade221 and blade 221 is designed to be laterally tiltable. over pivot point391 of operating stem 372 and fixed pivot point 351 unless preventedfrom tilting. laterally by contacts'32l pressing on stationary contacts171 of circuit terminals 161. In this form of my switch blade 221 isloosely and without operational friction prevented from lateral orlongitudinal horizontal movement in interior space 181 by polished pins341, 342 pressed into case halves 121, 131 and passing loosely throughholes 331, 332 in part 261 of blade 221.

When, in Fig. 5, stem 372 is pressed upward, section 261 of blade 221will go over center first striking pivot point 381' of stem 371 andcarrying it to the: position shown in Fig. 5 then bladeend 291 willleave'pivot'point 351 and move to pivot point 361 while blade end 281moves contacts 321 away from stationary contacts 171 and into contactwith stationary contacts 211 where they will stay until stem 372 isreleased and stem 371 is pressed downward to returnblade 221with'jcontacts 321 to their positions shown in Fig. 5.

Finally it should be' noted that for clear description the switch gaplengths are exaggerated'in the drawing. In actual practice my entireswitch maybe small with blade 22 only one-half inch wide, three quarterslong and about five mils thick. On open circuit the gap between themoving contacts and the stationary contacts may be four mils or lesssince there are always two gaps in series. Inoperation'the-blademovement is small therefore the velocity of themoving contacts will be small which is an ideal condition for allowinganalternating current to stop atzero voltage without restriking as thevoltage rises. It should also benotedthat maydouble break contactarrangement is best for breaking a direct current since the currentpaths through the two series gaps are parallel but opposite and themagnetic fields of the currents in the two g-aps repel each other toblow out the arcs at thegaps as the-switch opens. Tests have shownunexpectedly high circuit breakingcapacity for my switch on both A. C.and D; C. loads.

Having recited some of the objects of my invention, illustrated anddescribed two formsin which my invention may be practiced and explainedtheir" operation; I claim: I

l. Anelectric switch comprising a base memberv having a pair ofstationary electric circuit-1contactsinsulatedly secured thereontransversely symmetrically on opposite sides of a longitudinal centerline thereof, av movingcontact carrying. blade symmetrically alignedabout'its longitudinal center line transversely 'symmetrically with:said center line of said base member, a painof: electrically connectedmoving contacts carried on said, blade in..respective contact with saidstationary'contacts, a first pair of pivot point memberscarriedonsaidbase spaced from each other and from-said stationarycontacts on:said longitudinal center line ofsaidbase, said 'bladeaincluding aresilientv section= maintainedv bowed; in: longitudinal compression byan approximately planarztension section thereof, said blade beingloosely held against: substantial lateral or. longitudinal movement inthe.pl ane-' of said tension section by pin means through said bladeapproximately perpendicularly thereto-and: secured-in said base member,said pivot points individually and said stationary contacts togetherforming three longitudinally spaced fulcrum supports for said blade withone of saidsupports pressing against the center of said blade, ontheconvex side of said bowed compression member and theother two of saidsupports pressing the other side of said.blade at its respective ends,one of said'supports beingrnova'ble towards said blade to increase the.pressures. onisaid blade at said three supports to cause said bowed,section to go over center and b'owin the opposite direction, therebyrelieving all of said' fulcrumsupports. of. load and withdrawing bothsaid'moving' contacts from;contact with their respective mating contactssimultaneously.

2. The electric switch of claim 1 including a second pair of stationarycontacts carried on said base and spaced from said moving contacts onthe opposite side of said blade from said first pair of stationarycontacts and a second pair of pivot point members carried on said baseand positioned on the opposite sides of said blade respectively fromsaid first pair of pivot point members whereby when said movable one ofsaid first supports is moved to cause said bowed section of said bladeto go over center said blade will lift said moving contacts from saidfirst pair of stationary contacts and move said moving contacts intorespective contact with said second pair of stationary contacts and saidblade. will be sup-. ported on three other longitudinally. spacedfulcrum supiports'one determined by said second pair ofi'stationarycontacts and the other two determined respectively by said second pairof pivot'point members.

3. The electric switch. ofclaim' 2' in .which one of said three otherlongitudinally spaced fulcrum supports is movable towards said blade tocause said bowedacompression'member to go back over center to'return-said moving contacts into contact'with'said first pair ofstationary contacts and to return said blade to the support of saidfirstpair Qf'stationary contacts and" said first pair of pivot pointmembers.

4. Anelectric switch including a first pair of stationary contacts, apair ofinovable contacts in contact respectively with said first pair ofstationary contacts, a second. pair of stationarycontact's' spacedrespectively fromsaid movablecontacts on theopposite sideof said movablecontacts from 'saidJfirst' pair of stationary: contacts, a base.insulatedly supporting allsaid stationary contacts, a movableresilient.blade carrying said' movable contacts and having a center line in aplane midway betweenthe respective contacts of' each of saidpairsof'con-' tacts, said blade including, a resilientsection' and atensionsection for compressive endwise loading of said resilient sectionof said blade to bow said resilient section between its ends, afirstpair of pivot supportsfor said blade carried on said base alignedin saidplane on opposite sides of said blade, a second pair of pivotsupports for said' blade carried. onjsaid basealigned in said plane onopposite sides of said; blade. and one pivot sup port ofeach. f saidpairs being, spaced along said center line from the other pivot; supportof each of said pairs and from said contacts whereby when said blade isbowed in onedirection it will be supported near its'mid length on, itsconvex side and near its respective ends on its concave side. by saidfirst. pairof stationary contacts and the individual ones of said firstpair ofpivot supports and when said blade is bowed in the. otherdirection it will. be supported by said second pair of stationarycontacts and said individual ones of said' second. pair. of pivotsupports.

5. An electric switch structureincluding an electric switch and aswitchcase therefore: said electr-icswitch comprising a resilientmovable contact carrying blade formed with a pair of end sections,connected by. a pair of'side sections and a center-section laterallyseparated from said side sections, said side. sections being shorterthan said center section to bow said center section outwardly. from: theplane of saidsid'e sections, said blade including a pair of electricallyconnected movable contacts carried on one end thereof laterallysymmetrically spaced about the longitudinal center line thereof; saidcase including a first set of three fulcrum supports for said blade whensaid center section thereofis convexly bowedon one side of'said plane ofsaid side sections and a second set of three fulcrum supports for saidblade whensaid center section is convexly bowed on the other side ofsaid plane, said first set of three fulcrum supports. including. a firstset of two stationary contacts insulatedly secured insaid case onsaidone side. of said blade for respective contact with said movablecontacts on; said blade when said center'section of said blade is convexin one direction and a first pair of pivot points longitudinal ly spacedfrom each other and said first set of two stationary contacts, saidsecond set of three fulcrum supports including a second set of twostationary contacts insulatedly secured in said case on said other sideof said blade for respective contact with said movable contacts on saidblade when said center section is convex in the opposite direction and asecond pair of pivot points longitudinally spaced from each other andsaid second set of stationary contacts.

6. The electric switch structure of claim 5 in which said case includesa polished pin set/therein perpendicularly to said blade and said bladeis formed with a hole therethrough frictionlessly to receive said pin tomaintain said blade loosely rockable about both its longitudinal andtransverse centerlines on one of said pivots at the junction of saidcenterlines.

7. The switch of claim including operating means for passing said bowedcenter section of said blade through the plane of said side sections toreverse the side of said blade from which the center section is convexlybowed and thereby to move said blade from the support of one of saidsets of three fulcrum supports to the support of the other of said setof three fulcrum supports and move said movable contacts from contactwith said first set of two stationary contacts to contact with saidsecond set of two stationary contacts.

8. An electric switch structure including an electric case and anelectric switch operationally supported thereon, said electric switchincluding a resilient movable blade carrying a pair of electricallyconnected movable contacts transversely spaced on one end of said bladesymmetrically about the longitudinal center line thereof, said bladebeing separated by two laterally symmetrically spaced longitudinal slitsshorter than said blade into a center section and a surrounding sectionhaving two opposite end sections and two opposite side sections, saidtwo opposite side sections being shorter than said center section toplace said center section in longitudinal compression bowed convexlyaway from one side of the plane of said surrounding section, a firstpair of stationary contacts insulatedly secured in said case for matingcontact respectively with said movable contacts on the side of saidblade opposite the convexly bowed side of said center section, said caseincluding a first end pivot point positioned to contact said blade onits centerline on its same side with said stationary contacts and on itsend opposite said contacts, a first center pivot point positioned tocontact said blade between its ends on itscenterline on the convexlybowed side of said center section, whereby said blade will be supportedon said case by said first center pivot point on one side of said bladeand on theother side of said blade at one end by said first end pivotpoint and at the other end by said first two laterally spaced stationarycontacts, said blade being prevented from rocking about its longitudinalcenterline only by said first pair of stationary contacts.

9. The electric switch of claim 8 including first stern means formounting one of said pivot points in said case movably toward said bladeto pass said bowed center section through the plane of said surroundingsection to move said movable contacts away from said stationary contactssimultaneously.

10. The electric switch of claim 9 including a second pair of stationarycontacts secured on said case on the opposite side of said blade forsaid first pair, a second end pivot point on said case on the oppositeside of said blade from said first end pivot point, a second centerpivot point on said case on the opposite side of said blade from saidfirst center pivot point, whereby when said first stern means isoperated to pass said bowed center section through the plane of saidsurrounding section said blade will be stably supported on said one sideof said blade by said second end support and said second 8 pair ofstationary contacts and on the said other side of said blade by saidsecond center pivot point.

11. The electric switch of claim 10 including a second stem means formounting one of said pivot points in said case movably toward said bladeto pass said bowed center section through the plane of said surroundingsection from said'other side to said one side of blade.

12. The electric switch of claim 8 including means for preventing anysubstantial movement of said blade in its plane with respect to saidcase without interfering with the frictionless operation of said switch,which comprises a polished pin secured in said case approximatelyperpendicular to said blade and said pin positioned loosely through ahole formed in said blade to receive said pin.

13. In a substantially flat switch blade for overcenter operation tomove a pair of movable contacts carried on said blade from contact withone pair of stationary contacts to contact with another pair ofcontacts, means for lifting said moving contacts from their respectivelymating stationary contacts simultaneously which comprises a three pointisosceles triangular support means for said blade on one side thereofand a one point support means for said blade on the other side thereof,said triangular support means including said pair of stationary contactsand a first pivot point equidistant from said stationary contacts, saidone point support means including a second pivot point on a line fromsaid first pivot point to the midpoint of a line connecting saidsecondary contacts, and one of said pivot points being mounted movablytoward said blade to cause the overcenter operation thereof whereby whensaid one of said pivot points is moved toward said blade the pressure isincreased on the other of said pivot points and said contacts thereby tokeep said blade from lifting away from either of said stationarycontacts until it goes overcenter to lift away from both of saidcontacts at the same instant.

14. In the arrangement of claim 13 for lifting a pair of electricallyconnected moving contacts from a mating pair of stationary contacts forbreaking the circuit of said stationary contacts simultaneously at twoplaces the operationally frictionless means of stabilizing a switchblade in its plane while said blade is moved normal to said plane, saidfrictionless means comprising a stationary polished pin extendingsubstantially perpendicular to the plane of said blade and extendingloosely through a hole formed through said blade to receive said pin.

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